# What are the three main types of radioactive decay?

Apr 20, 2018

Well, there are four... here are simplified descriptions of them.

ALPHA DECAY

Emission of a helium-4 nucleus.

Example:

$\text{_(92)^(238) "U" -> ""_(90)^(234) "Th" + ""_(2)^(4) "He}$

This is favored for atomic number higher than $83$. Here the mass number drops by $4$ and atomic number drops by $2$.

BETA DECAY

A neutron splits into a proton and electron and emits the electron.

${\text{_(0)^(1) n -> ""_(1)^(1) p + }}_{- 1}^{0} e$

This is favored for an $\frac{N}{Z}$ ratio too high. This is the only one where the atomic number increases by $1$.

POSITRON EMISSION

A nuclide emits a positron, i.e. an electron-sized proton.

Example:

${\text{_(6)^(11) "C" -> ""_(5)^(11) "B" + }}_{1}^{0} e$

This is favored for an $\frac{N}{Z}$ ratio too low. This drops the atomic number by $1$ for light nuclei.

ELECTRON CAPTURE

A core electron absorbs into the nucleus and combines with a proton, forming a neutron.

$\text{_(1)^(1) p + ""_(-1)^(0) e -> ""_(0)^(1) n + "X-ray}$

This is favored for an $\frac{N}{Z}$ ratio too low. This drops the atomic number by $1$ but is favored by heavy nuclei.